Conventional contact mechanism assemblies for a circuit breaker use intermediate cam surfaces for transferring the contact torque/force from the stored energy components, such as, springs, to the contact arm in the ON position (contacts closed) and during the contact arm dynamical motion when acted upon by repulsion forces prior to getting locked in the blow-off position. Functional performance of such conventional mechanisms is typically affected by the friction between a rolling or a sliding component, which moves with the contact arm, and the intermediate cam surfaces along the entire trajectory. This results in a significant hysteresis, which is undesirable for the contact system as it brings inconsistency and can cause the contact force between the fixed and moveable contacts in the ON position to be compromised. As an important side effect, the mechanism performance becomes dependent on the wear condition of the cam surface. Furthermore, using the intermediate cam to achieve required torque at the contact arm in the ON position has a negative effect on the mechanism's over-travel performance and it results in substantial loss of a contact force/torque with erosion of the contacts.
Another observed issue with the existing prior art configurations is that in some of them the contact spring-cam mechanism is not physically protected and is substantially exposed. Therefore, it can be contaminated by flying particles (beads) during the short circuit shots.
Other conventional contact systems utilize locking cam surfaces arranged integrally with contact arm for latching it open in the blow-off position thus preventing from undesirable re-closing when the cam surfaces engage locking pins that are loosely attached to the crossbar. These types of configurations have demonstrated unreliability during latching of the contact arm at the end of its trajectory in the blow-open position.
U.S. Pat. No. 4,649,247 (Bernhard Preuss, et al.), the disclosure of which is incorporated herein by reference, discloses a contact mechanism assembly provided for current-limiting low-voltage circuit breakers. The contact mechanism assembly has a two-armed contact lever swivel-mounted on a central bearing pin whose lever arms are equipped at their ends with contact pieces. The contact lever is equipped with a slot for mounting on the bearing pin whose longitudinal axis extends approximately at a right angle to the longitudinal axis of contact lever. The contact lever has a stop extending at approximately a right angle to its longitudinal axis for a catch swivel-mounted on the bearing pin. The contact forces on both lever arms cannot be influenced by the swivel mount or by the drive mechanism of the contact lever, but are determined exclusively by the biasing springs.
U.S. Pat. No. 5,310,971 (Denis Vial, et al.), the disclosure of which is incorporated herein by reference, discloses a contact bridge of a molded case circuit breaker which is rotatably mounted in a bar by two springs arranged symmetrically from the rotation axis. Each spring is, on the one hand, anchored to the contact bridge, and, on the other hand, anchored to a rod housed in a notch of the bar. The same springs provide contact pressure and slowing-down of opening of the contact bridge at the end of repulsion travel by electrodynamic effect. The contact bridge bears on its edge cam surfaces which, at the end of opening travel, engage the anchoring rods to move them in the notches in the elongation direction of the tension springs. The energy of the contact bridge is thus taken up and stored in the springs causing slowing-down of the contact bridge. The profile of the cams can be chosen to enable reclosing of the contact bridge, this reclosing naturally being delayed by the slowing-down effect at the end of travel. The cam profile can also ensure latching of the contact bridge in the open position.
U.S. Pat. No. 7,005,594 (Yong-Gi Kim), the disclosure of which is incorporated herein by reference, discloses a movable contactor assembly of a circuit breaker capable of enhancing a current limiting function by maintaining a contact state between a movable contactor and fixed contactors in a closed circuit state, by preventing the separated movable contactor from returning towards the fixed contactors at the time of a current limiting operation, by accelerating a separation operation of the movable contactor from the fixed contactors at the time of a current limiting operation, and by continuously maintaining a separated state of the movable contactor from the fixed contactors until a trip operation is performed by a trip mechanism.
U.S. Pat. No. 7,145,419 (Yong-Gi Kim), the disclosure of which is incorporated herein by reference, discloses a contactor assembly for a circuit breaker comprises a first spring supporting pin, a cam plate, a second spring supporting plate, a link, and a spring. When a movable contactor is rotated without a rotation axis, a fluctuation of a rotation center of the movable contactor is not generated and a current limiting function is fast performed. Also, after contacts are separated from each other, the movable contactor is prevented from returning towards fixed contactors and the separated position is maintained for a predetermined time. An assembly process of the contactor assembly is simplified.
Thus, a need exists for an improved contact mechanism assembly for a circuit breaker.
This invention overcomes the problems of the prior art and provides an improved contact mechanism assembly for a circuit breaker.